This invention relates to Raney nickel alloy catalysts useful for hydrogenation reactions.
Raney nickel is a well-known hydrogenation catalyst which was described originally in U.S. Pat. No. 1,638,190 issued to Raney on May 10, 1927. Raney nickel is prepared by alloying nickel and aluminum and leaching out the aluminum with alkali to expose nickel as a finely divided porous solid in which form nickel is an effective hydrogenation catalyst.
Subsequently, improved nickel catalysts have been provided in the art by alloying various metallic constituents with the nickel and aluminum prior to the treatment with alkali. For example, in U.S. Pat. No. 2,948,687 issued to Hadley on Aug. 9, 1960, molybdenum is alloyed with nickel and aluminum and treated with alkali to provide a nickel-molybdenum alloy catalyst. The use of such catalysts either as finely divided powders or precipitated onto a support structure such as Al.sub.2 O.sub.3 is well known and such catalysts are widely used at the present time. However, it is also recognized that the use of these catalysts in either fixed bed or fluidized bed operations carries with them a number of constraints. For example, it is known that many of them are quite sensitive to small amounts of sulfur or carbon monoxide contamination in the feedstock. Also, when used in fluidized bed operations, the feedstock is subject to rather large pressure drops so that fairly rugged equipment is needed to move it through the bed. Lastly, many of these catalysts are sufficiently active so that if overheated during the reaction they will crack the carbonaceous feedstock and form coke on their surfaces with resultant significant decreases in activity. What is needed is a catalyst which, while retaining all of the advantages of high activity shown by Raney nickel, is not significantly affected by such operating conditions.
The catalytic reduction of an aromatic nitro compound such as dinitrotoluene to the corresponding amine-toluenediamine is a well-known and widely utilized industrial process. In many processes, such a reaction occurs at relatively low operating pressures and temperatures. However, when it is necessary to produce an alicyclic amine by saturating the underlying aromatic ring, the operating conditions become much more rigorous. Further, for amines in particular, it appears that prior art Raney catalysts are not widely utilized. Rather, catalysts based on noble metals--i.e. platinum--are normally used to accomplish this tranformation.